1. Field of the Invention
The instant disclosure relates to a catalyst composition; in particular, to an ethanol reforming catalyst composition with high catalytic activity and a preparation method of the ethanol reforming catalyst.
2. Description of Related Art
Approximately 80% of the world's energy demand is dependent on fossil fuel (oil, coal and natural gas, etc) which have limited availability in nature. Sustained consumption of fossil fuel will eventually lead to severe deficiency of energy and cause serious environmental pollution in the meantime. As a result, the use of non-polluting and renewable energy alternatives to fossil fuels is an inevitable trend. Also, the selection and use of new energy source must comply with conditions such as cleanliness, high efficiency, very low pollution and renewability.
Hydrogen energy is a clean and sustainably consumable alternative energy with high energy conversion efficiency. Hydrogen is a prospective carrier of energy due to the energy content per unit mass (i.e., 120.7 kJ/g) which is larger than that of other fuels; it also burns cleanly without emitting pollutants to our environment. As a result, the popularity of hydrogen energy can significantly improve the energy shortage problem worldwide and reduce pollution to the environment. For example, the hydrogen fuel cell is a small size, high efficiency, and low pollution (main emission is water) device, which may achieve continuous operations with stable supply of fuels (hydrogen and oxygen). In recent years, advanced development of the hydrogen fuel cell technology has readily driven the demand for hydrogen. The chemical energy conversion efficiency of hydrogen can now be achieved up to 45˜60% which is much higher than the heat engine efficiency (15%) of general internal combustion engine.
Scientists from multiple countries are hence devoted to investigate the appropriate hydrogen sources as a reproducible fuel due to the increased demand for hydrogen. Currently, methanol, ethanol, natural gas, naphtha and other hydrocarbons are mainly used as alternative hydrogen sources, of which ethanol possess the advantages of relatively high fuel quality, cheap price, convenience, ease of storage and transportation, and hydrogen generation at a relatively low reaction temperature of 200˜400° C. Comparing hydrogen energy with traditional gasoline fuel, the generated carbon dioxide (CO2) is reduced approximately 50%. Also, NOx, SOx, hydrocarbons, and other pollutants are eliminated.
Currently, there are four main reactions for hydrogen generation via ethanol as follow:
I. Ethanol Decomposition (ED)Chemical reaction: C2H5OH→H2+CH4+CO
II. Partial Oxidation of Ethanol (POE)Chemical reaction: C2H5OH+ 3/2O2→3H2+2CO2 
III. Steam Reforming of Ethanol (SRE)Chemical reaction: C2H5OH+3H2O→6H2+2CO2 
IV. Oxidative Steam Reforming of Ethanol (OSRE)Chemical reaction: C2H5OH+½O2+2H2O→2CO2+5H2 
Among the above reactions, reactions II, III, and IV are, in particular, the main focuses in academic researches. Steam reforming of ethanol is a reaction that applies high temperature heating and catalytic reaction to a water/ethanol mixture to produce hydrogen. Application of the oxidative steam reforming of ethanol provides another process to produce hydrogen under a lower temperature. The addition of oxygen affects the reforming process of ethanol to an exothermic reaction, and hence, the energetic exhaustion can be reduced. According to the chemical equations above, for each mole of ethanol, no more than 5 moles of hydrogen can be produced, thus, the maximum hydrogen selectivity is 167%. It is known in the prior technology that metals such as rhodium, ruthenium, platinum, palladium, iridium, and nickel can be used as catalysts to carry out catalytic reactions of ethanol while cerium oxides and zirconium oxides can be used as co-catalysts for the metal catalysts mentioned above.
In 2004, Schmidt group published a literature (G. A. Deluga, J. R. Salge, L. D. Schmidt, X. E. Verykios, Science, 2004, 303, 993-997.), in which high hydrogen selectivity are illustrated, based on the aforementioned reaction. In the literature, rhodium-cerium oxide is used as a catalyst, and 100% ethanol conversion and 116% hydrogen selectivity can be obtained. While the catalytic process is assisted by a second-stage catalyst, platinum-cerium oxide, the hydrogen selectivity can be further increased to 130%.
Currently, materials that can be applied to the oxidative steam reforming of ethanol for hydrogen production are quite limited besides cerium oxides. In 2009, Andrew T. Hsu and his team researched and developed a material having spinel structure, NiAl2O4—FeAl2O4 (refer to L. H. Huang, J. Xie, W. Chu, R. R. Chen, D. Chu, A. T. Hsu, Catal. Commun., 2009, 10, 502-508.), by which the hydrogen selectivity can achieve up to as high as 130% at 700° C. Although NiAl2O4—FeAl2O4 catalyst can provide excellent reactivity, the applicable temperature range is too high and therefore becomes an economically unsound solution in the long run.
Furthermore, international publication no. O2/078840 reveals a modified catalyst which is formed by a manganese oxide support having at least one metal selected from the group consisting of rhodium, ruthenium, platinum, palladium, iridium and nickel. Japanese publication no. 2003-265963 discloses a catalyst including a support having manganese oxide that has at least one metal selected from the group consisting of rhodium, ruthenium, platinum, palladium, iridium and nickel. The publications firstly apply at least one chlorine-containing compound, decompose with an alkaline aqueous solution, and then rinse the modified catalyst with water to remove chloride atoms.
Although the modified catalysts mentioned as above possess high reactivity, in terms of strength, and durability, improvements are still needed; production cost is relatively high, which is not suitable for commercial applications. Moreover, during steam reforming reaction of ethanol, the catalysts prepared by traditional impregnation preparation method, coke is readily produced which reduces the usable life of the catalysts.
To address the above issues, the inventor strives via associated experience and research to present the instant disclosure, which can effectively improve the limitation described above.